Safety device for machine tools using photoelectric tubes



2,340,548 SAFETY DEVICE FOR MACHINE TOOLS USING/ PHOTO-ELECTRIC TUBES S.MlKAMl Feb. 1,1944.

Filed Aug. 9, 1940 INVENTORQ Patented Feb. 1, 1944 SAFETY m-zvrcn FORMACHINE 'rooLs USING rno'ronmormc TUBES Shinkuro Mikami, Tokyo. Japan:vested Alien Property Custodian in the Application August 9, 1940,Serial No. 352,036

3 Claims.

My invention relates to improvements in a safety device for machinetools using photo-electric tubes for controlling the operation ofdriving motors and has for its object to provide a simple and positivesafety device for protecting a machine tool by stopping the feedingoperation immediately in case of accidents in a driving to be machinedare mechanically interconnected so that if one stops by some cause theother also is stopped. But the cutting tool is not directly connected tothe shaft of the motor for driving the cutting tool, these usually beinginterposed gearings, friction clutches and the. like power transmittingmechanism. Accordingly the mechanical interconnection of the drivingmotors can not perfectly protect the machine tools when the cutting toolis stoppeddue to the slip of the clutch mechanism or other causesoccurred in the intermediate driving mechanism.

My invention is specially designed to stop the feeding operation of amachine tool easily and positively by using photo-electric tubes'whenthe cutting tool is stopped owing to some causes in the driving gearitself.

In the accompanying drawing, Fig. 1 is an elevation of a milling planerdrawn diagrammatically combined with a device embodying my inventhroughthe lenses l5, l5 and l6, IE to the photo-electric tubes l1 and I8 whichcooperate to stop the feeding motor 8 by means of an electro'-magneticdevice I9 connected in the output circuit of-the photo-electric tubes l1and I8. 20 represents an enerigizing source of the photoelectric tubes.The interrupter I2' is provided with a' number of slots 2| arranged on acircle at equal distances apart. The light beams projected through thelenses l5 and it from the light source II are passed through thesuccessive slots 2| on the interrupter I2 when it is revolving and arefocussed through the lenses l5 and'lG' into the photo-electric tubes l1and I8 altemate- 1y which then conduct electric currents in the outputcircuit of the photo-electric tubes and energize the relay l9 by thecombined eifect of both photo-electric tubes. The relay I9 is arrangedto control a solenoid 24 which operates the main switch of the workfeeding motor 6' to be stopped in case of accident. A plurality ofphotoelectric tubes and I8 and the light-source l4 should be so arrangedwith regard to the interrupter I2 that either one or both of the lightbeams 22 and 23 can not pass through the same or more slots 2| when theinterrupter I2 is stationary. I g

In the above described arrangement of this invention, under the normaloperation of the machine tool the photo-electric tubes [1 and I8 conductsuflicient current. alternately within a very short time interval sothat the relay l9 may be effectively energized to operate the solenoidtion and Fig. 2 is a diagrammatic view of a photoelectric controllingdevice for use with the machine tool embodying my invention.

Referring to the drawing, l represents a base frame of the millingplaner having a working table 2, on which a work 3 to be machined isfixed. 4 represents a cutting tool and 5 is a main screw shaft mountedon the machine frame I and meshing with a half-nut secured to thesliding table 2 and is driven by a motor 6 through suitable gearmechanism for efiecting the feeding operation of the table. Thecuttinggtool 4 is driven by a motor 8 through a friction clutch 9 andgear wheels l0 and H.

According to my invention I provide a light interrupter l2, secured to asuitable shaft l3 in the driving mechanism between the friction clutch 9and the cutting tool 4 to control the light beams projected from a lightsource l4 alternately 24 of the motor switch and maintain the motor 6 inoperation. But if there occurs slip in the friction clutch 9 due to somefailure in the driving mechanism of .the cutting tool the disc I2 istarded suddenly due to some failure in the driving mechanism.

Iclaim:

1. A safety device for machine tools using photo-electric tubescomprising in combination a light controlling disc secured to a part ofthe driving mechanism of the cutting tool to be rotated therewith, saiddisc having a number of slots arranged on a circle, a plurality of photoelectric tubes connected to operate electrically, a light source andoptical devices to project light beams into said photo-electric tubesthrough the slot of said light controlling disc, a relay connected tothe output circuit of said photo-electric tubes to be effectivelyenergized by the cooperation thereof to control the operation of the vwork feeding motor of the machine tool, said light controlling discbeing so designed and arranged that when one of the photo-electric tubesis fully illuminated another one is fully shadowed.

2. A safety device for machine tools as claimed in claim 1, having twophoto-electric tubes con--' nected in parallel circuits to cooperatewith said light source and optical devices to project the saidphoto-electric tubes from said light source through said opticaldevices.

3. The apparatus as claimed in claim 1 inwhich the driving mechanism ofthe cutting tool includes a friction clutch and the light controllingdiscs is mounted on said driving mechanism between said clutch and thetool.

SHINKURO MIKALH.

